Apparatus for inducing controlled vibration in a specimen



Nov. 9, 1954 H. P. KOEHLER APPARATUS FOR INDUCING CONTROLLED VIBRATION IN A SPECIMEN 2 Sheets-Sheet 1 Filed May 5 1951 INVENTOR H. P. KOE-HLER Nov. 9, 1954 H. P. KOEHLER 2,693,696

APPARATUS FOR INDUCING CONTROLLED VIBRATION IN A SPECIMEN Filed May 5, 1951 2 Sheets-Sheet 2 INVENTOR United States Patent APPARATUS FOR INDUCING CONTROLLED VIBRATION IN A SPECHVIEN Harold Peter Koelller, Toronto, Ontario, Canada, as-

signor to A. V. Roe Canada Limited, Malton, Ontario, Canada, a corporation Application May 5, 1951, Serial No. 224,818

1 Claim. (Cl. 73-67) This invention relates to apparatus for determining the behaviour of specimens and materials under vibratory loading.

Existing theory on vibratory and fatigue stresses in unsymmetrical bodies is either unreliable or does not lend itself to practical application and consequently design requirements are usually based on empirically acquired data. As a result considerable emphasis has been placed on the development of test apparatus suitable for obtaining this data, and to date this development has been directed primarily towards apparatus operating on magnetic and electrical principles although such apparatus is necessarily complex, and to be tested in it a specimen must either be composed (at least in part) of a metal which lends itself to electromagnetic processes or it must have some such metal attached to it. Attaching extraneous material to the specimen is highly undesirable, however, since it introduces indeterminant stresses which alter the fatigue characteristics of the specimen and defeat the prime requisite of this type of testexact reproduction under test conditions of the vibratory loading encountered during actual operation. This requirement explains the unsatisfactory results obtained by attempting to reproduce induced vibration in a specimen with a device in which the loading is applied by mechanical means, and it also underscores the importance of mounting the specimen in the test apparatus just as it would be mounted for actual operation so that irrelevant stresses are not introduced.

It is the object of this invention to provide improved apparatus for inducing vibration of desired frequency and amplitude in a specimen.

It is a further object of the invention to provide, in an apparatus for applying vibratory loading to a specimen, means for mounting the specimen and for applying loading without altering the specimens natural mode of vibration.

It is a further object of the invention to provide apparatus for determining and inducing the natural mode of vibration in a specimen.

it is a still further object of the invention to provide apparatus adapted to apply vibratory loading to a specimen having either magnetic or non-magnetic properties without modifying the specimen.

Further objects will become apparent from examination of the following description and drawings of a particular example of the invention. In these drawings like reference characters denote like parts throughout, and

Fig. 1 represents a plan View of an apparatus, constructed in accordance with the invention, for testing the vibratory loading in compressor and turbine blades, with the guard removed from around the rotatable disc for greater clarity, and

Fig. 2 illustrates a. side elevation of the apparatus taken in the direction of arrow A in Fig. 1.

Referring now to the drawings, the apparatus comprises a frame supporting a nozzle 11, a blade-mounting chuck 12 and a disc-shaped member 13.

The disc 13 is carried by a shaft 14 journalled in bearings 15 and driven by a motor 16 regulated by a control 17. Evenly spaced aroundthe rim of the discs periphery there is a series of irregularities formed by radially directed notches or apertures 18, each notch being the full thickness of the disc and having two of its sides substantially parallel. A guard 19 (shown in Fig. only) is provided to protect the operator from the rotating disc. I

The nozzle 11 which is fixed to the frame with its ax1s parallel to the axis of the shaft terminates in a mouth 20 2,693,696 Patented Nov. 9, 1954 located in proximity to the notched portion of the disc 13. This mouth is rectangular in cross section and is so disposed that the long side of the rectangle is parallel to the base of the supporting frame 10. The width of the rectangle is less than the distance between the parallel sides of each of the notches 18 in the disc. Air is supplied to the nozzle by a pump (not shown) through a supply line 21 in which there is a regulating valve 22.

The plane of rotation of the disc divides the supporting frame 10 into two portions, one of which carries the nozzle 11 and the other the blade-mounting chuck 12. The chuck is mounted on a plate 23 adapted for positioning on the frame in the directions indicated by the double arrows B in Fig. l, and it carries a set of jaws 24 sup ported on rotatable spindles 2S and 26, the one spindle 26 being parallel to the axis of the shaft 14 and the other spindle 25 being perpendicular thereto. The jaws 24 are shaped to conform to the root shape of the specimen blade 27 to be tested, and alternative sets of jaws are provided to accommodate blade roots of differing configuration. The jaws may be removably mounted on the spindle 25 or the spindle 25 may be removable and replaceable by another spindle carrying another set of jaws.

When a blade is to be tested in the apparatus a set of jaws 24 conforming to the root of the blade 27 is placed in the chuck 12 and the blade mounted therein; the chuck is then positioned by adjusting the position of the plate 23 to bring the blade into alignment with the axis of the nozzle 11 and by turning the spindles 25 and 26 the blade is brought into the desired angular position relative to the air stream. The disc 13 is then rotated at constant speed and the valve 22 opened so that a stream of air is ejected from the nozzle.

This stream of air is directed by the nozzle onto the periphery of the adjacent face of the disc and as each of the notches 18 on the disc comes into alignment with the stream in turn, it admits the air which accordingly impinges on the blade, imposing a fluid dynamic load thereon. As the notch passes out of alignment, the fluid stream on the blade is interrupted by the solid peripheral frequency of the loading, and thus indirectly the frequency of vibration of the blade.

It will be apparent to those skilled in the art that apparatus of the type described can be used both for testing a specimen under conditions duplicating those encountered in actual operation, and for determining the behaviour of a specimen under conditions of resonance.

When actual operating conditions are to be reproduced, for instance conditions affecting a blade in a gas turbine engine, the chuck is located to give the blade the same position relative to the stream from the nozzle that it would have to the relative air stream in its actual installation, in a gas turbine engine and the mass flow of the air through the nozzle 11 is regulated by the valve 22, thus controlling the momentum of the specimen due to the applied loading and hence the amplitude of the blades vibration (at non-resonant frequencies); if desired, a more accurate control over the pressure and velocity of the air stream emerging from the nozzle may be provided in order to reproduce more closely conditions of actual operation; moreover, by regulation of the discs speed of rotation through the control 17 it is possible to duplicate the frequencies of the vibration induced in the blade by actual operation at various speeds.

When it is desired to study the behaviour of the blade at the critical frequency, that is at the resonant frequency where the blade is vibrating in its natural mode, the chuck is positioned so that the impinging air stream will produce the maximum amplitude of vibration in the blade for a given loading, and the discs speed regulated until resonance occurs in the blade as indicated by a sharp increase in the amplitude of vibration.

'odi c nature to the loading, streamy nre'frequeney of 4 It is to be understood that the form of the invention and a control for selectively regulating the rate of mass herewith shown and described is to be taken as a preferred flow of the fluid stream. example of the same and that various changes may be made in the shape, size and arrangement of the parts References Cited in the file of this patent Without departing from the spirit of the invention or the scope of the subjoined claim. UNITED STATES PATENTS What I claim as my invention is: Number Name Date Apparatus for inducing controlled vibration in a speci- 1,322,506 Austin Nov. 25, 1919 men, said apparatus comprising mounting means for hold- 2,330,416 Gibbs Sept. 28, 1943 ing the specimen, a nozzle for directing a stream of fluid 10 2,554,212 Quinlan May 22, 1951 ornto the 1speciiieiil, a disc rotatably moungediintelrlmediate 2,570,081 Szczeniowski Oct. 2, 1951 t e nozz e an t e mounting means, sai isc aving a plurality of spaced annularly disposed apertures for pe- FOREIGN PATENTS riodically admitting the fluid stream on the specimen, Number Country Date means for rotating the disc, a control for selectively 5 579,529 Germany June 28, 1933 rggulatingnth e speed of rotation of the disc rotating means 471,316 Great Britain Sept. 1, 1937 and hence for regulating the frequency of fluid admission, 575,917 Great Britain Mar. 11, 1946 

